1. Field
The invention generally relates to communication systems, and more particularly to improving the data rate of mobile data and the quality of channel estimation in an ATSC-M/H (Advanced Television Systems Committee—Mobile/Handheld) transport data stream.
2. Related Art
ATSC transport data stream content and function is described in U.S. patent application Ser. No. 11/276,473, entitled “APPARATUS, SYSTEMS AND METHODS FOR PROVIDING ENHANCEMENTS TO ATSC NETWORKS USING SYNCHRONOUS VESTIGIAL SIDEBAND (VSB) FRAME SLICING”, filed Mar. 1, 2006 and U.S. Pat. No. 7,532,677, entitled “APPARATUS, SYSTEMS AND METHODS FOR PRODUCING COHERENT SYMBOLS IN A SINGLE FREQUENCY NETWORK”, which issued on Sep. 27, 2007, both of which are hereby incorporated by reference in their entirety. In an ATSC-M/H transport data stream, transport data packets containing data for stationary (or “fixed” or “main stream”) receivers and transport data packets containing data for M/H receivers are transmitted. As shown in FIG. 3, the data structure of an ATSC-M/H transport data stream is organized in ATSC-M/H data frames each containing 5 ATSC-M/H sub-frames. Each ATSC-M/H sub-frame is subdivided into 16 ATSC-M/H slots, where each slot contains 156 transport data packets. An ATSC-M/H slot (i.e., 156 transport data packets) can be filled with data for stationary receivers. Alternatively, an ATSC-M/H slot may contain 118 transport data packets with data for M/H receivers and 38 transport data packets of data for stationary receivers. The 118 transport data packets containing data for M/H receivers are referred to as an M/H group and a collection of M/H groups is referred to as an M/H parade which can carry one or two M/H ensembles. Each M/H ensemble represents a logical pipe for IP based datagrams of one television (TV) program or service.
The M/H ensembles carried by the M/H parades include a specific number of ATSC-M/H slots in an ATSC sub-frame. Also, a potential mobile TV carrier holding a FCC License outside the broadcast band (e.g., channels 2-51) may wish to use ATSC M/H. This mobile TV carrier is not restricted by the FCC in the use of bandwidth in the ATSC-M/H transport data stream and is not required to transmit a specific minimum rate of TV data for stationary receivers as are normal ATSC broadcasters (e.g., channel 2-51). Nevertheless, a TV carrier intending to transmit only data for M/H receivers is limited by the requirements of the current ATSC-M/H standard which defines the data structure of the ATSC-M/H transport data stream. If each ATSC-M/H slot of the M/H ensemble containing only data for stationary receivers is substituted by an ATSC-M/H slot containing a combination of 118 transport data packets for M/H receivers and 38 transport data packets for stationary receivers, only 75% of the total bandwidth can be used for transmitting data for M/H receivers.
As shown in FIG. 1, an ATSC-M/H slot of a coded ATSC-M/H transport data structure is organized in regions A, B, C and D, where each region contains one or more segments. Only region A provides training sequences (i.e., known symbol sequences to aid the M/H receiver's equalizer in channel estimation and to track fading channels known to exist in the mobile environment). The regions B, C and D are positioned symmetrically around region A do not provide training sequences. As a result, the transmission quality of an ATSC-M/H transmission is reduced in regions B, C, and D. Thus, in a time varying transmission channel the channel estimation, the signal equalization and the subsequent decoding is downgraded in time periods corresponding to the occurrence of segments in regions B, C and D in the ATSC-M/H transmission data stream.
What is needed is a method for increasing the total possible data rate available for M/H mobile services and improving the quality of channel estimation in an ATSC-M/H by introducing additional training sequences in transport data stream.